Characterization of commercial RO membranes for the concentration of ammonia converted to ammonium sulfate from anaerobic digesters

Abstract

Commercially available thin film composite (TFC) polyamide membrane (GE AG) and asymmetric cellulose acetate membrane (GE CE) have been characterized using different concentrations of ammonium sulfate, up to 40g·l−1, in order to determine their suitability for the concentration of ammonium as ammonium sulfate from anaerobic digester digestate. At the manufacturer specified pressures of 1550kPa and 2900kPa, the solvent permeances for the GE AG and the GE CE membranes were found to be 2.1×10−5 and 7.4×10−6l·m−2·h−1·Pa−1, respectively. These permeances were practically independent of feed concentration. At the same time, both membranes showed excellent solute rejections, which decreased slightly with feed concentration, but were generally greater than 0.99. Consequently, the lower pressure GE AG membranes were considered to be more suitable for the separation of ammonium sulfate, and they were further tested at pressures exceeding the manufacturer specified value. These experiments revealed a slight decrease in solvent permeance for up to 17%, as well as a slight decrease in solute rejection, which was 0.97 or greater. Given these results, both membranes studied in this research are suitable for future investigations; first using multi-ion aqueous solutions and then pre-treated anaerobic digester digestate.